Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, monolithic windows, and/or the like. In certain example instances, designers of coated articles often strive for a combination of high visible transmission, substantially neutral color, low emissivity (or emittance), low sheet resistance (Rs), low U-values in the context of IG window units, and/or low specific resistivity. High visible transmission and substantially neutral color may permit coated articles to be used in applications where these characteristics are desired such as in architectural or vehicle window applications, whereas low-emissivity (low-E), low sheet resistance, and low specific resistivity characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors.
Low-E coatings having at least one silver based IR reflecting layer are known in the art. For example, see U.S. Pat. Nos. 5,344,718, 6,576,349, 8,945,714, 9,371,684, 9,028,956, 9,556,070, 8,945,714, 9,028,983, which are all hereby incorporated herein by reference. Low-E coatings on glass are widely used in commercial and residential buildings to save energy. The double Ag low-E coating is a dominant low-E product due to its excellent low emissivity properties and excellent control of solar heat gain.
However, conventional low-E coatings with silver IR reflecting layer(s) have problems associated with chemical durability and/or environmental durability which limit their applications. A reason is that the silver IR reflecting layers are not very stable, especially for double silver type low-E coatings. Once the Ag is decayed or damaged, the silver's optical, electrical, and thermal (emissivity) properties are degraded. For example, a solar control low-E coating with stack of glass/Si3N4/NiCr/Ag/NiCr/Si3N4 provides efficient solar control, but cannot reasonably survive chemical environments such as HCl acid environmental conditions. While there are some durable low-E coatings in the market, their performances are poor especially with respect to undesirably low light-to-solar gain ratio (LSG) values of around 1.0 or less. The higher the LSG value, the more energy saved. LSG is calculated as Tvis/SHGC, where SHGC is according to NRFC 2001.
Example embodiments of this invention solve these problems by providing a low-E coating that has improved silver durability (e.g., chemical durability), while maintaining high LSG values. Example embodiments of this invention relate to a coated article including an infrared (IR) reflecting layer of silver that is doped in order to improve characteristics of a low-E coating including such a layer. In certain example embodiments, a silver (Ag) based IR reflecting layer(s) is doped with a combination of silicon (Si) and aluminum (Al). In certain example embodiments, the IR reflecting layer may be of or include AgSiAl, or alternatively is Ag doped with Si and zinc (Zn), or Ag doped with a combination of Si, Zn and copper (Cu). It has surprisingly been found that a silver based IR reflecting layer doped with Si and Al, or Si and Zn, or Si, Zn and Cu, provides for improved corrosion resistance and chemical durability of the layer and the overall coating, and improved stability such as reduced haze upon optional heat treatment (HT), while maintaining good optical properties such as high LSG values of at least 1.10 (more preferably at least 1.20, and sometimes at least 1.30), compared to an Ag IR reflecting layer that is not doped. Doping SiAl into an Ag based IR reflecting layer can improve stack chemical durability while maintaining good optical properties. Such low-E coating may be used in applications such as monolithic windows, insulated glass (IG) window units, and the like.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer on the glass substrate; a first contact layer on the glass substrate over at least the first dielectric layer; an infrared (IR) reflecting layer comprising silver that is doped with Si and Al, the IR reflecting layer being on the glass substrate located over and directly contacting the first contact layer; a second contact layer on the glass substrate located over and directly contacting the IR reflecting layer; a second dielectric layer on the glass substrate located over at least the first and second contact layers and the IR reflecting layer; and wherein the coating has a sheet resistance (Rs) of no greater than 11 ohms/square and a normal emissivity (En) of no greater than 0.2.
In an example embodiment of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: a first dielectric layer on the glass substrate; a first contact layer on the glass substrate over at least the first dielectric layer; an infrared (IR) reflecting layer comprising silver that is doped with Zn and Si, the IR reflecting layer being on the glass substrate located over and directly contacting the first contact layer; a second contact layer on the glass substrate located over and directly contacting the IR reflecting layer; a second dielectric layer on the glass substrate located over at least the first and second contact layers and the IR reflecting layer; and wherein the coating has a sheet resistance (Rs) of no greater than 11 ohms/square and a normal emissivity (En) of no greater than 0.2.